For various reasons, it may be desirable to place a mark or a code on an object, such as an identification mark or code. Such a mark or code might be useful, for example, in identifying such articles if they are stolen, or for inventory control.
This marking could have specialized information, such as, words, insignias, logos, brand names, personalized signatures, date or batch codes, numbers, trademarks, company logos, and the like.
Another use of such a mark or code is in certain retail industries, such as the limited distribution cosmetic and fragrance industry. In such industries, distribution of products is limited to certain authorized retailers. However, it is known that some authorized dealers "divert" a portion of their stock to unauthorized dealers. Manufacturers therefore code each product package so that if it is diverted, the manufacturer can determine the identity of the authorized dealer who was the intended recipient of the package when it was shipped by the manufacturer. The manufacturer can then stop doing business with that dealer, or take other action against him.
Similarly, in other industries many products are packaged in transparent containers of glass or plastic and there has been a desire for many years to provide containers of this type with a method of marking such that once a mark has been applied, the mark cannot be easily removed. Such a method of marking would have obvious anti-counterfeiting applications but would also allow for the application of a code specific to each container and so would facilitate product tracking.
Laser marking of packages has been around for quite a few years. However, practical cost savings and environmental benefits are fully exercised when laser marking of packages is done in high-volume production processes.
CO.sub.2 lasers have traditionally been the industry standard for laser marking. These lasers are primarily used for marking of plastic package surfaces, including Integrated Circuit package. In this process a laser beam is directed through a copper stencil to form the mark characters. However, advances in die shrinkage have led to smaller and more compact IC packages on which the quality and visibility of CO.sub.2 markings is no longer adequate.
Yttrium aluminum garnet (YAG) laser markers have been seen as a possible alternative for marking. The YAG marking process works by steering the laser beam with a pair of X and Y galvanometers, controlled by software and hardware interfaces. Alphanumeric characters are scribed onto the package surface with the fine resolution and mark clarity needed for smaller plastic surface areas. A wide range of marking variables, such as depth, width and orientation can also be accommodated.
YAG lasers have also been used on ceramic packages, since the short wavelength of the laser easily penetrates the hard ceramic surface. The problem, however, has been that the YAG marking speeds are much slower than the CO.sub.2 marking speeds, since the YAG laser movement is limited by software interfacing and the mechanical response time of the optics. Because of this, YAG lasers have not been commonly used for high-volume production.
European Patent Application No. 472,049 (UCC) discloses a method for engraving cells in a solid surface. An alternative basin shaped cell has a bottom relatively flat. This is achieved by using a pulsed laser beam which imparts a pattern of equidistant engraved cells, each of increased volume. The pulses of the laser beam are formed in a series of consecutive groups of two or more pulses. Each cell is produced by at least two consecutive spaced-apart pulses.
However, this invention relates to a method and an apparatus for encoding or marking of objects for identification purposes. More particularly, this invention relates to an apparatus and method for using a laser to place a microscopically or macroscopically visible mark or code on the surface of an object.